xiii, b, 5 Haughivout: Flagellated and Ciliated Protozoa 243 



the epithelium. But with the flagellates, whose habitat would 

 certainly not seem to be normally in the tissues, the case is dif- 

 ferent. Entamoeba, Balantidium, and the flagellates evidently 

 find suitable conditions for life in both the lumen of the intes- 

 tine and in the tissues and prosper to a greater or lesser extent 

 in either place. If they show a preference, it seems to be in 

 favor of the lumen of the intestine. With the coccidia the 

 performance of tissue invasion is obviously in line with the 

 regular life cycle; with the flagellates and possibly with Enta- 

 moeba and Balantidium, tissue parasitism appears to be in the 

 nature of a departure from the normal. 



In Coccidium, for example, sporogony seems to fill the dual 

 purpose of protoplasmic rejuvenescence (through fertilization) 

 and the dissemination of spores. It seems to supervene upon 

 sexual maturity and lowered protoplasmic vitality, and yet cases 

 have been reported of chronic coccidiosis, in which the host 

 became virtually a carrier, producing a constant stream of 

 spores of the parasite, which obviously meanwhile continues 

 its schizogonous cycle. Is this a matter of chemical adjustment 

 between host and parasite? 



Calkins's classical experiments with Paramcecium show the 

 effects of artificial stimulation on the metabolism and reproduc- 

 tive rate of Protozoa and are merely an illustration of the effects 

 that may be produced upon a protozoon by altered environmental 

 conditions. These chemical changes may be, in the future, found 

 to exert a more profound influence on the activities of parasites 

 than we now realize. In 1914 I suggested (21) the possibility that 

 relapses of malarial fevers might be brought about by a tran- 

 sient glycsemia, the blood sugar furnishing the rejuvenating 

 stimulation. At the time I had in mind the work of Calkins 

 on Paramcecium and that of Bass and Johns on the cultivation 

 of Plasmodium. This view has been more recently expressed 

 by Calkins, (5) who has suggested that the change may be, as 

 I myself have long held, in the nature of the equivalent of fer- 

 tilization, a process of the restoration of lost vitality, a substitu- 

 tion of a labile for a stabile condition of the protoplasm. Ex- 

 perimental evidence, as I have stated, points strongly to the 

 belief that such a condition of protoplasmic rejuvenation can 

 be brought about artificially within certain limits. 



While we have so far no direct evidence of the invasion of 

 the human tissues by the intestinal flagellates or flagellates of 

 that type, unless we include Ross's observation of "cercomonads" 

 having several flagella and an undulating membrane and tricho- 



